I also have a user receiving this error whenever the user updated a meeting and added another attendee (single user or Distribution List).
User has Outlook 2003 SP2 with The current patch for DST is KB942763. The prior patch was KB933360.
I have doen the following:
- removed Outlook's cached mode
- re-synched ost/nk2/oab files by deleting files from D:\Documents and Settings\UserProfile\Local Settings\Application Data\Microsoft\Outlook\Outlook.ost
and also D:\Documents and Settings\UserProfile\Application Data\Microsoft\Outlook\Outlook.nk2
- deleted the Outlook profile and noticed the profile in the registry hadn't been removed:
HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows Messaging Subsystem\Profiles\Outlook
- Recreated the profile